One question: Why on earth would a champion other than supports would go deep into the Utility Tree since it's guaranteed that they will have a lot less defensive stats and offensive stats. Which are pretty much mandatory on any tank/bruiser/burst-mage/AD carry?

This specifically has changed. You are correct Lifesteal didn't really belong in the offense tree. Lifesteal and Spellvamp are now bundled into the same mastery inside Utility. While it may not be popular among AD carry players to lose the LS from the offense tree, Utility as a whole has been made a more attractive choice for all character types.

Lol? lifesteal quints were only good on 1 champ. Warwick Jungle. You start W, and you can start boots and never use a single hp pot.

Spellvamp quints were only good on 1 champ as well. Mundo Jungle. It helps you sustain early and it procs on smite.

Both of these strategies consider that your team is bad and doesn't leash for you. And these are the only times you would get these expensive runes optimally. Again, I tried this all in PBE. So don't be like "I don't listen to lvl 24 smurfs".